Selective Hydrogen Production from Formic Acid Decomposition on Pd–Au Bimetallic Surfaces

Abstract

Pd-Au catalysts have shown exceptional performance for selective hydrogen production via HCOOH decomposition, a promising alternative to solve issues associated with hydrogen storage and distribution. In this study, we utilized temperature-programmed desorption (TPD) and reactive molecular beam scattering (RMBS) in an attempt to unravel the factors governing the catalytic properties of Pd-Au bimetallic surfaces for HCOOH decomposition. Our results show that Pd atoms at the Pd-Au surface are responsible for activating HCOOH molecules; however, the selectivity of the reaction is dictated by the identity of the surface metal atoms adjacent to the Pd atoms. Pd atoms that reside at Pd-Au interface sites tend to favor dehydrogenation of HCOOH, whereas Pd atoms in Pd(111)-like sites, which lack neighboring Au atoms, favor dehydration of HCOOH. These observations suggest that the reactivity and selectivity of HCOOH decomposition on Pd-Au catalysts can be tailored by controlling the arrangement of surface Pd and Au atoms. The findings in this study may prove informative for rational design of Pd-Au catalysts for associated reactions including selective HCOOH decomposition for hydrogen production and electro-oxidation of HCOOH in the direct formic acid fuel cell.

Effect of annealing in oxygen on alloy structures of Pd–Au bimetallic model catalysts

“…52,[56][57][58] The growth of the Pd overlayer on the Au(111) surface at 77 K has been suggested to obey a layer-by-layer mechanism. 52,[56][57][58] The growth of the Pd overlayer on the Au(111) surface at 77 K has been suggested to obey a layer-by-layer mechanism.…”

Graphene-supported small tungsten carbide nanocrystals promoting a Pd catalyst towards formic acid oxidation

“…1,2 Oxidation of formic acid is generally accepted to take place through a parallel or dual pathway mechanism: [3][4][5] (1) the direct dehydrogenation pathway, which involves removal of two hydrogen atoms (dehydrogenation) to form CO 2 , HCOOH / CO 2 + 2H + + 2e À ; (2) the indirect dehydration pathway, consisting of a dehydration step to yield water and adsorbed CO, followed by oxidation of CO to CO 2 at high potential, HCOOH / CO ads + H 2 O / CO 2 + 2H + + 2e À . 1,2 Oxidation of formic acid is generally accepted to take place through a parallel or dual pathway mechanism: [3][4][5] (1) the direct dehydrogenation pathway, which involves removal of two hydrogen atoms (dehydrogenation) to form CO 2 , HCOOH / CO 2 + 2H + + 2e À ; (2) the indirect dehydration pathway, consisting of a dehydration step to yield water and adsorbed CO, followed by oxidation of CO to CO 2 at high potential, HCOOH / CO ads + H 2 O / CO 2 + 2H + + 2e À .…”

“…Pt and Pd are two of the most effective electrocatalysts for the formic acid oxidation. Several approaches exist to further increase the formic acid oxidation efficiency of Pd: (1) alloying to combine the merits of Pd with other metals, including Pd-Pt, 12 Pd-Au, 5,14 Pd-Cu, 15,16 and Pd-Ni; 17 (2) building specic shape, architecture and structural arrangement, such as core-shell structure, 18 Pd nanochain networks, 19 three dimensional palladium nanoowers 20 and Pd nanorods,; 21 (3) developing better catalyst supports to disperse these nanostructures to prevent aggregation and maximize electrocatalytic activity of Pd, with graphene as an excellent choice due to its huge surface area, high electrical conductivity, and excellent catalytic activity; 8,22 (4) adding co-catalyst to the catalyst system, through which a strong electronic interaction between them may lead to better performance, e.g. [9][10][11][12][13] This consideration together with its lower cost and higher abundance leads Pd to more research attention recently as the primary catalytic metal.…”

Microwave-Assisted Synthesis of PdxAu100–x Alloy Nanoparticles: A Combined Experimental and Theoretical Assessment of Synthetic and Compositional Effects upon Catalytic Reactivity

“…This allows for tuning and optimization of surface chemical reactivity via charge-transfer, 12−13 d-band mixing, [14][15] and lattice strain effects. 15 On a more localized level, geometric ensemble effects (dependent on specific arrangements of discrete groups of atoms) are also known to be important in 13,[15][16][17][18] lower temperatures than is required using conventionally-heated (convective; CvH) methods. 37 Alloy…”